wifi: rtw88: Set AMPDU factor to hardware for RTL8814A

Tell the chip the maximum AMPDU size supported by the AP. This greatly
improves the TX speed of RTL8814AU in the 2.4 GHz band. Before: ~90
Mbps. After: ~300 Mbps.

Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/4edc2a63-81b3-431c-9a37-5a7d899a6cc2@gmail.com